The extant gobioid fishes form a highly diverse group comprised of eight families and over 2000 species. They pose many taxonomic and phylogenetic challenges, particularly when working with fossils. Here we introduce dagger Simpsonigobius gen. nov., a new freshwater gobioid of small size (<= 34 mm) from the Lower Miocene of Turkey, and analyse its relationships using a total evidence phylogenetic framework from a previous study that we have significantly improved and expanded upon. dagger Simpsonigobius gen. nov. exhibits a unique combination of characters, including five branchiostegal rays, a palatine with a weakly 'T'-shaped head, an additional ray in the anal fin relative to the second dorsal fin, and rounded-to-quadrangular otoliths with a pronounced posterodorsal projection. Undated and tip-dated analyses in a total evidence Bayesian framework, utilizing our updated and expanded data set (48 extant in-group species, 10 fossil species, 48 morphological characters, data from five genes), indicate its relationship with the Oxudercidae, which is reinforced by our comparative morphological analysis. Our results reveal dagger Simpsonigobius gen. nov. as the oldest skeleton-based member of the Oxudercidae and the oldest freshwater species of the clade Gobiidae + Oxudercidae. The tip-dating analysis estimates divergence ages for Gobiidae (34.13 Ma) and Oxudercidae (34.83 Ma), which are in accordance with previous node-dating analyses. Additionally, based on our time-calibrated tree, we conduct the first reconstruction of ancestral habitat types employing stochastic character mapping and incorporating fossil taxa. The outcome reveals that the ancestor of the Gobioidei likely did not exclusively inhabit freshwater environments, challenging previous assumptions and emphasizing the importance of considering combined habitat types among early-splitting extant taxa. Our study represents the first simultaneous analysis of fossil and extant gobioid species, along with dating of the tree, and our data emphasize the ability of this approach to place gobioid fossils within a reliable chronological and phylogenetic context. http://zoobank.org/urn:lsid:zoobank.org.pub:5000841F-1836-43D8-BE75-4C090A478566
